Microlens array, image display apparatus, object apparatus, and mold

ABSTRACT

A microlens array includes N lenses ranging from a 1 st  lens to an N th  lens and a lens arrangement area. N is a positive integer. The lens arrangement area has the N lenses arranged in array. The lens arrangement area receives light emitted from a light source. An i th  (i being 1 st  to N th ) lens satisfies a conditional expression below: 
       −20°≤θ≤20°
         where   θ denotes an angle formed by a main-axis orientation of double refraction and a reference orientation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a division of U.S. patent application Ser.No. 15/719,213 filed Sep. 28, 2017, which is based on and claimspriority pursuant to 35 U.S.C. § 119(a) to Japanese Patent ApplicationNo. 2016-188937 filed Sep. 28, 2016, and Japanese Patent Application No.2017-181894 filed Sep. 22, 2017 in the Japan Patent Office, the entiredisclosures of each of which are hereby incorporated by referenceherein.

BACKGROUND Technical Field

Embodiments of the present disclosure relate to a microlens arrayelement, an image display apparatus, an object apparatus, and a mold.

Background Art

An image display apparatus, such as a heads-up display (HUD), is knownto include a screen member, such as a microlens array element.

The screen member, for example, a microlens array element, has room forimprovement in optical characteristics.

SUMMARY

In one aspect of this disclosure, there is provided an improvedmicrolens array including N lenses ranging from a 1^(st) lens to anN^(th) lens (N is a positive integer) and a lens arrangement area havingthe N lenses arranged in array. The lens arrangement area receives lightemitted from a light source. An i^(th) (i is 1^(st) to N^(th)) lenssatisfies a conditional expression below:

−20°≤θ≤20°

where

θ denotes an angle formed by a main-axis orientation of doublerefraction and a reference orientation.

In another aspect of this disclosure, there is provided an improvedapparatus including a light source to emit the light, an image formingelement to form an image with the light emitted from the light source,and the above-described microlens array. At least a part of the lensarrangement area is irradiated with the light for forming the image.

In still another aspect of this disclosure, there is provided animproved object apparatus including the above-described apparatus, andan object equipped with the apparatus.

In yet another aspect of this disclosure, there is provided an improvedmicrolens array including a plurality of lenses, a lens arrangement areahaving the plurality of lenses arranged in array, and a gate areaadjacent to the lens arrangement area. The gate area has a width thatincreases in a direction that approaches the lens arrangement area in aplanar view. In further aspect of this disclosure, there is provided animproved apparatus including a light source including a light source toemit light, an image forming element, and a screen. The light ispolarized. The image forming element forms an image with the lightemitted from the light source. The screen has N (N being a positiveinteger) lenses arranged in array. The screen has an optically effectivearea through which the light for forming the image passes. The N lensesranging from a 1^(st) lens to an N^(th) lens,

an i^(th) lens (i being the 1^(st) to the N^(th)) of the screensatisfying a conditional expression below:

−20°≤θ≤20°

where

θ denotes an angle formed by a main-axis orientation of doublerefraction and a polarization direction of the light beam.

In still further aspect of this disclosure, there is provided animproved mold for producing a microlens array by injection moldingincluding a lens section and a gate section. The lens section forms alens arrangement area, in which a plurality of lenses is arranged, of amicrolens array. The gate section lets resin in the lens section. Thegate section has an inner wall that manner increases in width in adirection that approaches the lens section in a planar view.

In still further aspect of this disclosure, there is provided animproved method of displaying an image including generating polarizedlight, irradiating the polarized light through a screen including aplurality of lenses in an array, and displaying an image using thepolarized light which has passed through the screen. Each of theplurality of lenses satisfies:

−20°≤θ≤20°

where

θ denotes an angle formed by a main-axis orientation of doublerefraction and a polarization direction of the polarized light.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other aspects, features, and advantages of thepresent disclosure will be better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIGS. 1A through 1C are illustrations of an image display apparatusaccording to one embodiment of the present disclosure;

FIGS. 2A and 2B are illustrations of diverging light emitted from amicro-convex lens and the occurrence of coherent noise;

FIGS. 3A through 3C are illustrations for describing the elimination ofthe coherent noise;

FIGS. 4A through 4C are illustrations of three examples of array formsof micro-convex lenses;

FIGS. 5A through 5D are illustrations of five examples of array forms ofmicro-convex lenses;

FIGS. 6A and 6B are illustrations of anamorphic micro-convex lenses;

FIGS. 7A and 7B are illustrations of two examples of microlens arrayelements;

FIG. 8 is an illustration of a randomly-arranged lens array;

FIG. 9 is a perspective view of a lens arrangement area of a microlensarray element as an example;

FIGS. 10A through 10D are illustrations of a procedure for producing amicrolens array element according to a comparative example by moldinginjection;

FIGS. 11A through 11D are illustrations of a procedure for producing amicrolens array element according to an embodiment of the presentdisclosure by injection molding;

FIGS. 12A and 12B are plan views of the microlens array elementaccording to the comparative example and the microlens array elementaccording to the embodiment of the present disclosure, respectively;

FIGS. 13A and 13B are illustrations of the presence and absence ofdeformation in lens arrangement areas of the microlens array elementaccording to the comparative example and the microlens array elementaccording to the embodiments of the present disclosure, respectively;

FIG. 14 is an illustration of a microlens array element having a curvedlens arrangement area that is treated same as a microlens array elementhaving a flat lens arrangement area;

FIGS. 15A through 15C are illustrations for describing how to determinewhether the white color is achieved at a plurality of points in the lensarrangement area of the microlens array element when a virtual image isformed based on image data of the white color;

FIG. 16 is a graph for describing a relation between retardation and theorientation of the optic axis when a virtual image is formed based onimage data of the white color by using the microlens array elementaccording to the comparative example;

FIG. 17 is an illustration of a chromaticity map of Ua-Va chromaticitycoordinates measured in a virtual image formed based on the image dataof the white color using the microlens array element according to thecomparative example;

FIG. 18 is a graph for describing a relation between retardation and theorientation of the optic axis when a virtual image is formed based onimage data of the white color by using the microlens array elementaccording to the embodiments of the present disclosure;

FIG. 19 is an illustration of a chromaticity map of Ua-Va chromaticitycoordinates measured in a virtual image formed based on the image dataof the white color using the microlens array element according to theembodiment of the present disclosure;

FIGS. 20A through 20C are illustrations of microlens array elementsproduced using improved molds according to variations;

FIG. 21 is an illustration of a shift in orientation of the optic axis.

The accompanying drawings are intended to depict embodiments of thepresent disclosure and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected and it is to be understood that eachspecific element includes all technical equivalents that have the samefunction, operate in a similar manner, and achieve similar results.

Although the embodiments are described with technical limitations withreference to the attached drawings, such description is not intended tolimit the scope of the disclosure and all of the components or elementsdescribed in the embodiments of this disclosure are not necessarilyindispensable.

A HUD is known that includes an image forming unit that forms an imageand an optical system that project the image onto a windshield of amobile object such as a vehicle so as to display a virtual image of theimage.

Such a HUD forms an intermediate image, and enlarges the intermediateimage using a screen member such as a diffuser panel or a microlensarray element to form a virtual image in the above-described process.

Particularly when a semiconductor laser is used as a light source, someHUDs employ a microlens array element that contributes to reducing orpreventing the occurrence of speckle noise to relatively prevent theblurring of a virtual image.

The microlens array element is typically formed by injection molding,using thermoplastic resin. Such a microlens array element is greatlyinvolved with double refraction. The semiconductor laser is known toemit a light beam that is linearly polarized light. In a microlens arrayelement that is insusceptible to double refraction, the linear polarizedlight does not change in state between before and after the linearlypolarized light passes through the microlens array element. However, ina microlens array element that has a great effect of double refraction,the linear polarization light changes to elliptically polarized light,which changes the ratio of p polarized light relative to s polarizedlight, i.e., extinction ratio. The extinction ratio differs according tothe wavelength of a semiconductor laser even when the double refractionis common. Accordingly, when any desired color is to be generated for avirtual image by using three semiconductor lasers having differentwavelengths, a target value of light-intensity balance (power balance)is not obtained. Thus, any desired color is not generated.

Particularly, when the double refraction is uneven in theoptically-effective area of the microlens array element, thelight-intensity balance is not successfully adjusted. In the presentdisclosure, the “optically-effective area” refers to the beam-passingarea (area through which the beam passes), in which an image to be avirtual image is formed, in the microlens array element. Theoptically-effective area corresponds to at least a part of the lensarrangement area in the microlens array element.

To handle such a circumstance, a configuration is proposed in whichretardation (phase difference) of double refraction is less than orequal to 0.098 times the wavelength of light emitted from a laser lightsource.

According to the Jones vector, the polarized light that has passedthrough the microlens array element 8 is obtained by the followingformula where θ denotes the tilt (which is referred to also as a “shift”or a “variation” in orientation of the optic axis) of the optic axiswith reference to the polarization direction of linearly polarized light

$\quad\begin{pmatrix}1 \\0\end{pmatrix}$

emitted from a laser light source:

$\begin{pmatrix}x \\y\end{pmatrix} = {{T_{\theta,ɛ}\begin{pmatrix}1 \\0\end{pmatrix}} = {\begin{pmatrix}{\cos \; \theta} & {{- \sin}\; \theta} \\{\sin \; \theta} & {\cos \; \theta}\end{pmatrix}\begin{pmatrix}{\exp ( {i\; \frac{ɛ}{2}} )} & 0 \\0 & {\exp ( {{- i}\; \frac{ɛ}{2}} )}\end{pmatrix}\begin{pmatrix}{\cos \; \theta} & {\sin \; \theta} \\{{- \sin}\; \theta} & {\cos \; \theta}\end{pmatrix}\begin{pmatrix}1 \\0\end{pmatrix}}}$

With a reduction in value of ε, the values of Tθ and ε are approximatelyan identity matrix. Accordingly, the linearly polarized light remainsthe same between before and after the light passes through the microlensarray element.

However, the retardation is very difficult to control with the moldingconditions, such as the pressure applied to a mold and the temperatureof a mold, and the injection speed of resin. Such a control depends onthe physical properties of the thermoplastic resin used.

As a matter of course, there is nothing to be concerned about when themicrolens array element is used in the HUD. However, the presentinventors have determined that such a thermoplastic resin has adifficulty in, e.g., having a coat to increase transmittance,particularly when mounted on a vehicle.

In other words, the present inventors have determined that the typicalmicrolens array element has room for improvement in increasing theoptical properties.

Hence, the present inventors have conceived of the following embodimentsof the present disclosure.

FIGS. 1A-1C illustrate selected portions of an image display apparatusaccording to an embodiment of the present disclosure.

An image display apparatus 1000 described with reference to FIG. 1A is aheads-up display which displays a two-dimensional color image.

The image display apparatus 1000 is mounted, for example, on a mobileobject such as a vehicle, an aircraft, and a ship, and makes navigationinformation used for operating the mobile object (for example, speed andmileage) visible through a transmission and reflection member 10 (forexample, a front windshield) of the mobile object. In the followingdescription, an XYZ three-dimensional orthogonal coordinate system thatis set to the mobile object (i.e., a coordinate system that moves withthe mobile object in a synchronized manner) is referred to. Note thatthe term “transmission and reflection member” indicates a member thattransmits some rays of the incident light and reflects at least some ofthe remaining incident light.

In FIG. 1A, a light source unit 100, also referred to as a light source,emits a pixel displaying beam LC for displaying a color image in +Zdirection.

The pixel displaying beam LC is one beam in which beams of three colorsincluding red (R), green (G), and blue (B) are combined.

More specifically, the light-source unit 100 is configured, for example,as illustrated in FIG. 1B.

In FIG. 1B, semiconductor lasers RS, GS, and BS, which form a lightsource, emit laser beams (linearly polarized light) of red, green, andblue (RGB), respectively. In the present example embodiment, laserdiodes (LD), which are also referred to as end-surface emitting lasers,are used as the semiconductor lasers RS, GS, and BS. Alternatively,vertical cavity-surface emitting lasers (VCSEL) may be used as thesemiconductor lasers RS, GS, and BS, instead of the end-surface emittinglasers.

As illustrated in FIG. 1B, coupling lenses RCP, GCP, and BCP control thedivergence of the laser beams emitted from the semiconductor lasers RS,GS, and BS.

The laser beams of RGB colors whose divergence has been controlled bythe coupling lenses RCP, GCP, and BCP are shaped by apertures RAP, GAP,and BAP. More specifically, the diameters of the laser beams of RGBcolors are controlled by the apertures RAP, GAP, and BAP.

The shaped laser beams of RGB colors enter the beam combining prism 101.

The beam combining prism 101 includes a dichroic film D1 that transmitsthe R light and reflects the G light, and a dichroic film D2 thattransmits the R and G light and reflects the B light.

Accordingly, a single laser beam in which the laser beams of RGB colorsare combined is emitted from the beam combining prism 101.

The emitted laser beam is converted by a lens 102 into a “collimatedbeam” having a prescribed laser-beam diameter. This “collimated beam”corresponds to the pixel displaying beam LC.

Note that the intensity of the laser beams of RGB colors that make upthe pixel displaying beam LC is modulated according to the image signal(i.e., image data) of a “two-dimensional color image” to be displayed.The intensity modulation may be performed through direct modulation inwhich the semiconductor lasers are directly modulated or throughexternal modulation in which the laser beams emitted from thesemiconductor lasers are modulated.

In other words, the light-emission intensity of each of thesemiconductor lasers RS, GS, and BS may be modulated by a driving unitas a controller according to the image signal of RGB components.

The pixel displaying beam LC that is emitted from the light source 100is directed towards a two-dimensional deflector 6 that serves as animage forming element, and is two-dimensionally deflected.

In the present example embodiment, the two-dimensional deflector 6 is aminute mirror that moves on a pivot that is formed by “two axes that areorthogonal to each other”.

More specifically, the two-dimensional deflector 6 includesmicro-electromechanical systems (MEMS) that include minute pivotingmirrors formed by semiconductor processes or the like.

However, no limitation is intended thereby, and the two-dimensionaldeflector 6 may be, for example, combinations of two minute mirrors thatpivot on a single axis in the directions that are orthogonal to eachother.

The pixel displaying beam LC that has been two-dimensionally deflectedas above travels towards a concave mirror 7, and is reflected to amicrolens array element 8.

In other words, the optical effect of the concave mirror 7 is to correctthe deformation of an image formed on the transmission and reflectionmember 10 by the two-dimensionally deflected pixel displaying beam LC.

The pixel displaying beam LC that is reflected at the concave mirror 7shifts in parallel according to the deflection performed by thetwo-dimensional deflector 6, and enters the microlens array element 8 toscan the microlens array element 8 two-dimensionally. In the presentembodiment, the microlens array element 8 serves as a screen member or ascreen.

This two-dimensional scanning forms a “two-dimensional color image” onthe microlens array element 8.

As a matter of course, what is displayed on the microlens array element8 is “only the pixels that are being irradiated by the pixel-displayinglight beam LC at that time”. A two-dimensional color image is formed asa “set of pixels that are momentarily displayed” realized bytwo-dimensional scanning using the pixel displaying beam LC. A“two-dimensional color image” is formed on the microlens array element 8as described above, and the light of the image data on a pixel by pixelbasis enters the concave mirror 9 and is reflected.

The microlens array element 8 includes a “minute convex lensarrangement”, as will be described later. The concave mirror 9configures a “virtual image forming optical system”.

The “virtual image forming optical system” forms the magnified virtualimage 12 of the “two-dimensional color image”. The transmission andreflection member 10 is provided in front of the image forming positionof the magnified virtual image 12 to reflect the light beam forming themagnified virtual image 12 toward an observer 11 (an eye of the observeris illustrated in FIG. 1A) side. The observer 11 (for example, a driverof the mobile object) visually recognizes the virtual image at aprescribed position on the optical path of the laser beam reflected bythe transmission and reflection member 10. The observer 11 visuallyrecognizes the magnified virtual image 12 by the light reflected towardsthe observer 11 as above.

As illustrated in FIG. 1A, the up-down direction of the figure isdenoted by a “Y direction”, and the direction perpendicular to thedrawing is denoted by an “X direction”.

In FIG. 1A, the Y direction usually corresponds to the up-and-downdirections for the observer 11, and the Y-axis direction is alsoreferred to as a “vertical direction”. In FIG. 1A, the X directionusually corresponds to the right and left directions for the observer11, and the X direction is also referred to as a “lateral direction”.

As described above, the microlens array element 8 has a minute convexlens arrangement.

As will be described later, the minute convex lens arrangement has “aplurality of minute convex lenses (microlenses) that are closelyarranged at a pitch close to the pitch of pixels”.

Herein, the plurality of micro-convex lenses is two-dimensionallyarranged at a predetermined pitch along a plane (XY plane) perpendicularto the Z direction such that the convex surface becomes the incidentplane. As a specific array form thereof, there are a matrix-shaped array(square-matrix-shaped array) where the X direction is set as a rowdirection and the Y direction is set as a column direction and ahoneycomb-type array (zigzag array). As an example, the optic axis ofeach micro-convex lens is parallel to the Z-axis.

The planar shape (shape when viewed from the Z-axis direction) of eachmicro-convex lens is, for example, a circle, a regular N-gon (N is anatural number equal to or greater than 3), or the like. In the presentexample embodiment, it is assumed that the minute convex lenses haveequal curvature (radius of curvature).

Each of the minute convex lenses isotropically diffuses the pixeldisplaying beam LC. In other words, each of the minute convex lenses haseven diffusing power in all directions, if desired. Such “diffusingfunction” is briefly described below.

FIG. 1C illustrates four pixel displaying beams L1 to L4 that enter themicrolens array element 8, according to the present example embodiment.

The four pixel displaying beams L1 to L4 enter the microlens arrayelement 8 at the four corners of the two-dimensional pixel displayingbeam formed on the microlens array element 8.

As the four pixel displaying beams L1 to L4 pass through the microlensarray element 8, the pixel displaying beams L1 to L4 are converted intobeams L11 to L14. Assuming that a laser beam whose cross section is ahorizontally oriented quadrangle surrounded by the pixel displayingbeams L1 to L4, enters the microlens array element 8, such a laser beambecomes a “divergent laser beam whose cross section is ahorizontally-oriented quadrangle surrounded by the beams L11 to L14”.

The function of the minute convex lenses as described above is referredto as the “diffusing function”. The “divergent laser beam whose crosssection is a horizontally-oriented quadrangle surrounded by the beamsL11 to L14” is obtained by temporally collecting the pixel displayingbeam that has been converted into a divergent laser beam as describedabove.

The pixel displaying beam is diffused such that “the laser beamreflected at the transmission and reflection member 10 irradiates awider area in the proximity of the observer 11”.

When the diffusing function described above is not available, the laserbeam reflected at the transmission and reflection member 10 irradiatesonly a “small area in the proximity of an eye of the observer 11”.

For this reason, when the observer 11 moves his/her head and theposition of the eyes deviates from the “small area”, the observer 11 canno longer visually recognize the magnified virtual image 12. Bydiffusing the pixel displaying beam as described above, the laser beamreflected at the transmission and reflection member 10 irradiates a“wide area in the proximity of the observer 11”.

Accordingly, even if the observer 11 “slightly moves his/her head”, theobserver can visually recognize the magnified virtual image withreliability.

In the present embodiment, the pixel display beam LC enters themicrolens array element 8 as a parallel beam, and diverges after passingthrough the microlens array element 8.

In any image display apparatus that forms an image by scanning ato-be-scanned medium, such as a transmissive or reflective screen, withlaser light, speckle noise occurs due to strong interference of thelaser light as coherent light, so that a virtual image to be viewedirregularly flickers. To handle such a circumstance, a microlens array(micro-convex lens structure) in which a plurality of microlenses(micro-convex lenses) are arranged with a pitch close to the beamdiameter of the laser light is used as the to-be-scanned medium in thescanning image display apparatus. With the use of such a microlensarray, the intensity of the speckle noise is reduced while controllingthe divergence angle of the laser light in any desired degree, thusincreasing the visibility of a virtual image.

In the present embodiment, the microlens array element 8 has a“micro-convex lens structure” where a plurality of micro-convex lensesthat diffuse the pixel displaying beam LC are arranged to be in closecontact with each other at a pitch approximate to a pixel pitch”.

The micro-convex lens is larger than the “beam diameter of a pixeldisplaying beam LC”.

The minute convex lens is made larger than the “beam diameter of thepixel displaying beam LC” to reduce the coherent noise, as describedwith reference to FIG. 2 and FIG. 3.

FIG. 2A illustrates a microlens array element 802. The microlens arrayelement 802 has a micro-convex lens structure in which micro-convexlenses 801 (lenses or microlenses) are arranged. A laser-beam diameter807 of a pixel displaying beam 803 is equal to or smaller than a size(diameter) 806 of each micro-convex lens 801. In other words, the size806 of the micro-convex lens 801 is larger than the laser-beam diameter807.

Note that, the pixel displaying beam 803 according to the presentembodiment is a laser beam and has a light intensity distribution of aGaussian distribution around the center of the laser beam.

Accordingly, the laser-beam diameter 807 is a distance in the radialdirection of a laser beam where the light intensity in the lightintensity distribution decreases to “1/e2”.

In FIG. 2A, the laser-beam diameter 807 is drawn to have a size equal tothe size 806 of each micro-convex lens 801. However, in someembodiments, the laser-beam diameter 807 may not be equal to the size806 of the micro-convex lens 801.

The laser-beam diameter 807 is satisfactory as long as its size does notexceed the size 806 of each micro-convex lens 801.

In FIG. 2A, the entire pixel displaying beam 803 is incident on onemicro-convex lens 801 and is converted to a diffused laser beam 804having a divergence angle 805. Note that the “divergence angle” may bereferred to as a “diffusion angle” in some cases.

In FIG. 2A, one laser beam is diffused (the diffused laser beam 804)without any interfering laser beam, and thus no coherent noise (specklenoise) occurs.

Note that the size of the divergence angle 805 may be set by adjustingthe shape of the micro-convex lens 801 as appropriate.

In FIG. 2B, the laser-beam diameter of the pixel displaying beam 811 istwice the array pitch 812 of the micro-convex lenses, and the pixeldisplaying beam 811 enters both micro-convex lenses 813 and 814.

In this case, the pixel displaying beam 811 passes through the twomicro-convex lenses 813 and 814, thereby separating into two laser beams815 and 816 each of which diverges.

The two laser beams 815 and 816 overlap each other in an area 817 tointerfere with each other therein, so that coherent noise occurs.

In FIG. 3A, the pixel displaying beam 824 enters portions ofmicro-convex lenses 822 and 823 of the microlens array element 821.

The laser-beam diameter of the pixel displaying beam 824 is equal to thesize of the micro-convex lens 822 or the like. In this case, the beamportion incident on the micro-convex lens 822 becomes a dispersed laserbeam 826 to be diffused, and the beam portion incident on themicro-convex lens 823 becomes a dispersed laser beam 827 to be diffused.

The dispersed laser beams 826 and 827 are diffused in such a directionthat the beams 826 and 827 are separated away from each other, and thusthe beams 826 and 827 do not overlap each other. In such a state,coherent noise does not occur. In other words, if the beam diameter ofthe pixel displaying beam 824 is set to be equal to or smaller than thesize of the micro-convex lens 822, the coherent noise due to the laserbeams diffused by the micro-convex lens does not occur.

An example of specific numerical values of the diameter of themicro-convex lens and the beam diameter of the pixel displaying beamincident on the microlens array element is described. For example, thebeam diameter of the pixel displaying beam is easily set to be about 150μm.

In this case, the size of the micro-convex lens constituting themicro-convex lens structure is favorably set to be the above-describedsize of 150 μm or more, for example, 160 μm, 200 μm, or the like.

In the microlens array element 821 illustrated in FIG. 3A, themicro-convex lenses 822, 823, and so on are arranged, side by side,without gap.

Accordingly, a “width of the boundary portion (hereinafter, this may bereferred to as a “boundary width”) of the adjacent micro-convex lenssurfaces is 0”. For this reason, only the dispersed laser beams 826 and827 are generated from the pixel displaying beam 824 that enters themicro-convex lenses 822 and 823 as illustrated in FIG. 3A.

However, in an actually-formed micro-convex lens structure, there is nocase where the “boundary width between the adjacent micro-convex lensesis 0”.

In other words, similarly to the microlens array element 831 illustratedin FIG. 3B, in an actually-formed micro-convex lens structure, there isno case where the “width of a boundary portion 835 between micro-convexlenses 833 and 834 is 0”.

In the boundary portion 835 between the micro-convex lenses 833 and 834,microscopically, a “curved surface is formed to be smoothly continuous”,and thus, a curved surface is formed in the boundary portion 835.

If the pixel displaying beam is incident on this portion, the curvedsurface formed in the boundary portion 835 in this manner functions as a“microlens surface” with respect to the incident light.

Accordingly, the pixel displaying beam 832 incident across themicro-convex lenses 833 and 834 causes a dispersed laser beam 838 aswell as dispersed laser beams 836 and 837 to be generated. The dispersedlaser beam 838 occurs due to the lens function of the curved surface ofthe boundary portion 835 and overlaps and interferes with the dispersedlaser beams 836 and 837 in areas 839 and 840, so that coherent noiseoccurs.

FIG. 3C is a diagram illustrating “reduction and prevention of thecoherent noise” in a micro-convex lens structure, according to thepresent embodiment. In the micro-convex lens structure, a curved-surfaceshape itself of a boundary portion 843 where lens surfaces ofmicro-convex lenses 841 and 842 are gently connected forms a “microlenssurface”.

The radius of curvature of the curved-surface shape of the boundaryportion 843 is denoted by r as illustrated in FIG. 3C.

In the present embodiment, for the purpose of simplification, a pixeldisplaying beam incident on the micro-convex lens structure is referredto as a “wavelength-λ monochrome laser beam”. In a case where the radiusof curvature r of the boundary portion 843 is larger than the wavelengthλ of the pixel displaying beam (r>λ), the curved surface having a radiusof curvature r has a lens function on the incident pixel displayingbeam.

Accordingly, in this case, the beam component passing through theboundary portion 843 diverges and overlaps and interferes with the laserbeams diffused by the micro-convex lenses 841 and 842, so that coherentnoise occurs.

On the other hand, if the radius of curvature r of the boundary portion843 is smaller than the wavelength A, of the pixel displaying beam, theboundary portion 843 has a “sub-wavelength structure” with respect tothe pixel displaying beam.

As known in the art, the sub-wavelength structure does not cause a lensfunction on the “light having a wavelength larger than thesub-wavelength structure”. Accordingly, the boundary portion 843 havinga radius of curvature r smaller than the wavelength λ does not functionas a “lens” but straightly transmits the pixel displaying beam withoutdivergence.

Accordingly, the beam portion straightly passing through the boundaryportion 843 and the dispersed laser beams diffused by the micro-convexlenses 841 and 842 do not overlap each other, so that the coherent noisedue to interference does not occur.

In other words, the order among the beam diameter d of the pixeldisplaying beam, the wavelength λ, the size D of the micro-convex lens,and the radius of curvature r of the surface constituting the boundaryportion are favorably defined as follows.

D>d,λ>r.

In a case where the two-dimensional magnified virtual image which is tobe displayed is monochrome image, the pixel displaying beam is formed bymonochromatic coherent light having a wavelength λ.

Accordingly, in this case, the D, d, r, and λ are set so as to satisfythe above-described order, so that the coherent noise can be suppressed.Like the embodiment, in the case of displaying a two-dimensional colorimage (magnified virtual image), the pixel displaying beam LC is acombination of three R-color, G-color, and B-color beams.

When the wavelengths of the three beams are denoted by λR (=640 nm), λG(=510 nm), and λB (=445 nm), the order is that “λR>λG>λB”.

Accordingly, with a view to preventing coherent noise, the radius ofcurvature r of the surface constituting the boundary portion isfavorably set to be smaller than the shortest wavelength λB, forexample, to be 400 nm.

However, if the radius of curvature r is set to be smaller than thelongest wavelength λR (for example, to be 600 nm), the coherent noisedue to the R component of the image display beam can be prevented. Inother words, the coherent noise can be effectively reduced.

If “r (for example, 500 nm)<λG” is set, the coherent noise due to theR-component and G-component beams of the image display beam can beprevented.

In a case where the pixel displaying beam LC is a “combination of beamsof three colors of red, green, and blue (RGB)”, the coherent noiseoccurs independently with respect to the three color components.

The whole of the independent coherent noise due to the beams of threecolors of red, green, and blue (RGB) becomes visually-recognizablecoherent noise.

Accordingly, among the coherent noise due to three colors, if anycoherent noise due to one color disappears, the visually-recognizablecoherent noise is greatly improved, which contributes to improvement ofimage quality of an observation image.

Accordingly, with respect to the effect of prevention of coherent noise,the effect can be obtained in associated with only the“longest-wavelength R component” among the three color components, andnext, the “reduction effect” is improved in the order of the G componentand the B component.

Therefore, if the radius of curvature r is set to be smaller than thelongest wavelength λR (for example, to be 600 nm), in addition to thereduction of coherent noise, a certain effect can be achieved.

With respect to the visibility of the coherent noise, noise intensityvaries with the wavelength, the beam diameter, the multi/single modes,or the like, but in general, the visibility is increased in the order ofR≈G>B.

In other words, the visibility of a human eye is low with respect to thelight having a wavelength λB, and thus the coherent noise is difficultfor human eye to visually recognize. Accordingly, if the radius ofcurvature r is set to be smaller than the wavelength λG (for example, tobe 500 nm), the coherent noise due to the light having wavelengths λRand λG of which visibility is relatively high can be reduced.

Although the coherent noise due to the light having wavelength λB ofwhich visibility is low occurs, the coherent noise is not securelyvisually recognizable.

As a matter of course, if the radius of curvature r is set to be smallerthan the wavelength λB (for example, to be 400 nm), as described above,the coherent noise can be more effectively reduced.

Each size of the plurality of micro-convex lenses constituting themicro-convex lens structure is in the order of 100 μm as describedabove, and this can be implemented as a known “microlens”.

In addition, the micro-convex lens structure where the plurality ofmicro-convex lenses is arranged can be implemented as a “microlensarray”.

For this reason, the micro-convex lens is sometimes may be referred toas a “microlens”, and the micro-convex lens structure may be referred toas a “microlens array”.

As known in the art, the microlens array is manufactured by producing amold having a transfer surface of a lens surface array of the microlensarray and transferring a mold surface to a resin material by using themold.

With respect to formation of the transfer surface of the mold, there iswell known a method of forming the transfer surface by using cutting,photolithography, and the like.

In addition, the transferring of the transfer surface to the resinmaterial can be performed, for example, by injection molding.

The reduction of the radius of curvature of the boundary portion betweenthe adjacent microlenses can be implemented by reducing the boundarywidth.

The small boundary width can be implemented by “sharpening” the boundaryportion formed between the adjacent microlens surfaces.

In the mold for microlens array, as a method of reducing the size of the“boundary width between the adjacent microlenses” down to the order ofwavelength, there are known various methods.

In a comparative example, a method is described that includes increasingthe radius of curvature of each microlens by anisotropic etching and ionprocessing to remove non-lens portions of the boundary portion.

In another comparative example, a method is described that includesremoving a flat surface between adjacent microlenses by using isotropicdry etching.

For example, by using the above-described well-known methods, it ispossible to manufacture a microlens array where the radius of curvatureof the surface constituting the boundary portion between the adjacentmicrolenses is sufficiently small.

In other words, the above-described microlens array element can beconfigured as a microlens array having a structure where a plurality ofmicrolenses are arranged to be in close contact with each other.

By forming the microlens array where the radius of curvature r of thesurface constituting the boundary portion between the adjacentmicrolenses is smaller than 640 nm, the coherent noise due to the Rcomponent beam can be prevented.

In addition, by forming the microlens array where the radius ofcurvature r is smaller than 510 nm, the coherent noise due to the Rcomponent beam and the G component beam can be prevented.

By forming the microlens array where the radius of curvature r of thesurface constituting the boundary portion between the adjacentmicrolenses is smaller than 455 nm, the coherent noise due to the R, G,and B component beams can be prevented.

Previously, the image display apparatus (heads-up display) illustratedin FIG. 1A to FIG. 1C was described.

The concave mirror 7 illustrated in FIG. 1A to FIG. 1C has a “functionof removing the distortion of the image formed on the transmission andreflection member 10 by the pixel displaying beam LC which istwo-dimensionally deflected”.

In other words, the concave mirror 7 functions as a deflection rangerestriction means of restricting a scan range of the microlens arrayelement by adjusting a deflection range of the pixel displaying beamwhich is two-dimensionally deflected.

In a case where a deflection angle of the pixel displaying beam which istwo-dimensionally deflected by the two-dimensional deflector 6 is notgreatly large, the deflection range restriction means may be omitted.

Conditions of the micro-convex lens structure (microlens array) and themicro-convex lenses (microlenses) are the same as those described above.

In other words, a micro-convex lens structure is configured so that aplurality of micro-convex lenses which are equal to or larger than abeam diameter of a pixel displaying beam are arranged to be in closecontact with each other at a pitch approximate to a pixel pitch.

Herein, three examples of specific forms of the microlens arraysatisfying the conditions are illustrated in FIGS. 4A to 4C.

A microlens array 87 as a form example illustrated in FIG. 4A isconfigured so that square-shaped microlenses 8711, 8712, and so on orthe like are arranged in a square matrix shape.

The number of pixels of a two-dimensional image (magnified virtualimage) displayed in the heads-up display is determined by an arrangementcycle of the microlenses in the microlens array.

In the array of FIG. 4A, the distance between the centers of microlenses8711 and 8712 adjacent to each other in the X-axis direction is denotedby X1.

Moreover, in FIG. 4A, the distance between the centers of themicrolenses 8711 and 8721 adjacent to each other in the Y-axis directionis denoted by Y1. The X1 and Y1 can be regarded as an “effective size ofone pixel”.

In the following description, the “effective size of one pixel” may bereferred as an “effective pitch of one pixel” or an “effective pixelpitch”.

A microlens array 88 as a form example illustrated in FIG. 4B isconfigured so that regular hexagonal-shaped microlenses 8811, 8821, andso on are arranged to be in close contact with each other.

In the microlens array of this case, the arranged microlenses 8811 andthe like do not have sides parallel to the X-axis direction. In otherwords, since upper sides and lower sides of the microlenses arranged inthe X-axis direction have a “zigzag shape”, the array is called a“zigzag-type array”.

A microlens array 89 as a form example illustrated in FIG. 4C isconfigured so that regular hexagonal-shaped microlenses 8911, 8921, andso on are arranged to be in close contact with each other.

In the microlens array of this case, the arranged microlenses 8911 andthe like have sides parallel to the X-axis direction. The array of thiscase is called an “armchair-type array”. The zigzag-type array and thearmchair-type array may collectively be called a “honeycomb-type array”.

The armchair-type array illustrated in FIG. 4C is an array obtained byrotating the zigzag-type array illustrated in FIG. 4B by 90 degrees. Inthe zigzag-type array, X2 illustrated in FIG. 4B can be regarded as an“effective pixel pitch in the X-axis direction”, and Y2 can be regardedas an “effective pixel pitch in the Y-axis direction”.

In the armchair-type array, X3 illustrated in FIG. 4C can be regarded asan “effective pixel pitch in the X-axis direction”, and Y3 can beregarded as an “effective pixel pitch in the Y-axis direction”.

In FIG. 4B, the effective pixel pitch Y2 is a distance between thecenter of the microlens 8821 and the central point of the right side ofthe microlens 8811.

In FIG. 4C, the effective pixel pitch X3 is a distance between thecentral point of the side with which two microlenses contacting theright side of the microlens 8911 are in contact and the center of themicrolens 8911.

In the zigzag-type array, since the effective pixel pitch in the X-axisdirection X2 is small, the resolution in the image display in the X-axisdirection can be improved.

In addition, in the armchair-type array, the resolution in the Y-axisdirection can be improved.

As described above, by arranging the microlenses in a honeycomb type,the pixels which are smaller than an actual lens diameter can beeffectively represented, so that the number of effective pixels can beincreased.

As described above in the micro-convex lens structure (microlens array)of the microlens array element, the boundary portion between theadjacent microlenses has a radius of curvature r.

The radius of curvature r is smaller than, for example, the wavelengthλR of the R component of the pixel displaying beam.

Accordingly, as described above, the “coherent noise due to interferenceof the coherent light of the R component” is prevented.

However, if the radius of curvature r is larger than the wavelength AGof the G component beam and the wavelength λB of the B component beam ofthe pixel displaying beam, these beams are diffused in the boundaryportion to interfere with each other.

Accordingly, the coherent noise occurs due to the interference.

In this case, in the “square-matrix-shaped array” of FIG. 4A, thedivergence (diffusion) in the boundary portion occurs in two directionsof Xa and Ya directions of FIG. 4A, which causes the coherent noise.

By contrast, in the array of FIG. 4B, the divergence of the boundaryportion occurs in three directions 8A, 8B, and 8C. In the case of FIG.4C, the diffusion occurs in three directions 9A, 9B, and 9C.

In other words, in the square-matrix-shaped array, the divergence in theboundary portion occurs in two directions, and in the honeycomb-shapedarray, the divergence occurs in three directions.

Accordingly, in the square-matrix-shaped array, the coherent noiseoccurs in two directions, and in the honeycomb-shaped array, thecoherent noise occurs in three directions.

In other words, the generated coherent noise is “dispersed in twodirections” in a square-matrix-shaped array, whereas the generatedcoherent noise is “dispersed in three directions” in a honeycomb-shapedarray.

The maximum intensity of the coherent light generating the coherentnoise is constant.

Accordingly, as the number of dispersion directions becomes large, the“contrast of the generated coherent noise” can be allowed to be weak, sothat the coherent noise is difficult to visually recognize(inconspicuous).

Accordingly, in a case where the generation of the “coherent noise dueto the component having a wavelength smaller than the radius ofcurvature r of the boundary portion” is not allowed, the microlens arrayis favorably set to a “honeycomb-shaped array”.

When the boundary width is larger than the wavelength λR, the coherentnoise due to the coherent light of the R component is also generated.

However, the “boundary width between the lens surfaces” of the adjacentmicro-convex lenses is small, and the light energy of the coherent lightincident on the portion having a small boundary width is small.Accordingly, the light energy generating the coherent noise is notlarge.

Moreover, even if the coherent noise is generated, even in the case of ahoneycomb-shaped array, as described above, the coherent noise isdispersed in three directions, so that the contrast becomes weak.

Accordingly, the visibility of the coherent noise is effectivelyreduced.

As described with reference to FIG. 1A, a virtual image forming opticalsystem that forms the two-dimensional magnified virtual image 12 isconfigured with the concave mirror 9.

In other words, the magnified virtual image 12 is a set of pixel imagesformed by the concave mirror 9.

If the microlenses as the micro-convex lenses are allowed to have an“anamorphic function”, the diffusion function of the micro-convex lenscan be allowed to be different between directions perpendicular to eachother.

FIG. 6A and FIG. 6B are schematic diagrams each illustrating microlenses8 (micro-convex lenses) that are formed to be in close contact with eachother in the microlens array element 8. In the example of FIG. 6A, themicro-convex lenses have a vertically-elongated elliptic shape and arearranged in a matrix-shaped array (square-matrix-shaped array).

In the example of FIG. 6B, the micro-convex lenses 80 have verticallyoriented hexagon shapes having sides parallel to the X-axis directionand are arranged in an “armchair-type array”.

In the micro-convex lens 80, the radius of curvatures of the lenssurface are different between the X-axis direction and the Y-axisdirection, and the radius of curvature in the Y-axis direction Ry issmaller than the radius of curvature in the X-axis direction Rx. Inother words, the curvature of the micro-convex lens 80 in the X-axisdirection is greater than the curvature in the Y-axis direction.

Accordingly, the power (dispersing power) of the micro-convex lens 80 inthe X-axis direction is greater than the power (dispersing power) in theY-axis direction.

As the lens surface has curvatures in both of the X-axis direction andthe Y-axis direction, as illustrated in FIG. 6B, the micro-convex lenscan be formed to have a hexagon shape, so that the “visibility of thecoherent noise” can be weakened as described above.

FIG. 6A and FIG. 6B illustrate the cases where the pixel displaying beamLC enters one of the micro-convex lenses 80. In FIG. 6A and FIG. 6B, thewidth of each of the micro-convex lens 80 in the Y-axis direction iswider than the width in the X-axis direction.

As illustrated in FIG. 6A, the pixel displaying beam LC is formed as an“elliptic shape where the beam diameter thereof is long in the Y-axisdirection”, and the laser-beam diameter in the X-axis direction issmaller than the diameter of the micro-convex lens 80 in the Y-axisdirection.

In such a configuration, the pixel displaying beam LC can be allowed tobe “incident without crossing the lens boundary”, and the shape of thecross section of the emitting dispersed laser beams has a(horizontally-oriented) elliptic shape where the beam diameter is longin the X-axis direction.

If the curvature in the X-axis direction is greater than the curvaturein the Y-axis direction irrespective of the length of the micro-convexlens in the Y-axis direction and the X-axis direction, in thecross-section FX of a laser beam of the diverging beam emitted from eachmicro-convex lens, the diameter in the Y-axis direction is longer thanthe diameter in the X-axis direction. In other words, the beam ishorizontally oriented.

The HUD as described above may be provided, for example, for a vehiclesuch as a car, and the X-axis direction and the Y-axis directionindicate “the right and left directions with reference to a driver'sseat” and “the up-and-down directions with reference to the driver'sseat”, respectively.

In the present embodiment, the transmission and reflection member 10 isa front windshield of a vehicle. This windshield may be treated, ifdesired, in a conventional manner so that it can better display theimage provided from the heads-up display unit

According to the present example embodiment, for example, a “navigationimage” can be displayed ahead of the front windshield as the magnifiedvirtual image 12, and a driver as the observer 11 can observe such anavigation image without moving his/her line of vision away from theahead of the front windshield while staying in the driver's seat.

In such an embodiment, it is desired that the magnified virtual image bea “horizontally-oriented image when seen from a driver”, as describedabove. In other words, it is desired that the image formed on amicrolens and the magnified virtual image be an image whose angles ofview is wider in the X-axis direction.

It is also desired that “the viewing angle be wider in the lateraldirection than in the vertical direction” such that a driver as theobserver can recognize the displayed image even in a slanting directionfrom the right and left sides.

For this reason, a greater diffusion angle (anisotropic diffusion) isrequired for the longer-side direction (i.e., X-axis direction) of themagnified virtual image, with reference to the shorter-side direction(i.e., Y-axis direction) of the magnified virtual image.

Accordingly, it is desired that the minute convex lenses of themicrolens array element be anamorphic lenses whose curvature is greaterin the longer-side direction than in the shorter-side direction of animage formed on a microlens or a magnified virtual image, and that thediffusion angle of the pixel displaying beam be “wider in the lateraldirection than in the vertical direction of a two-dimensional image”.

As described above, according to the example embodiment of the presentdisclosure, the utilization efficiency of light and the brightness ofdisplay image can be improved as the light is dispersed to a minimumarea that satisfies the desired angle of view of a HUD.

As a matter of course, “isotropic diffusion” in which the diffusionangle is equal between the lateral direction and the vertical directionmay be applied instead of the “anisotropic diffusion” described above.

However, as long as a vehicle-installed HUD for a car or the like isconcerned, there are few cases in which the driver observes a displayedimage from up-and-down directions.

Accordingly, as long as a vehicle-installed HUD is concerned, it isdesired that the diffusion angle of the pixel displaying beam be “widerin the lateral direction than in the vertical direction of atwo-dimensional image” as described above in view of the utilizationefficiency of light.

Conventionally, it is known that the surface of a minute convex lens(microlens) can be formed as “aspherical surface”. The anamorphic lenshas “aspherical surface”, and the use of such an anamorphic lens enablesthe aspherical surface of a minute convex lens as desired. Moreover, theuse of the anamorphic lens can perform aberration correction. Due to theaberration correction, “nonuniformity in diffusion intensity” may bereduced.

Each of the micro-convex lenses (microlenses) in the micro-convex lensstructure (microlens array) FIG. 4A to FIG. 4C has a square shape or aregular hexagon shape.

The shape of the micro-convex lens is not necessarily a regular polygonshape as described above, but shapes obtained by stretching the shapesof the microlenses illustrated in FIG. 4A to FIG. 4C in one directionmay also be available.

In this case, the square shape becomes a “rectangle shape”, and theregular hexagon shape becomes an elongated deformed polygon shape.

With respect to the effective pixel pitch of the micro-convex lensstructure, in the arrays of FIG. 4A to FIG. 4C, the effective pixelpitches in the X-axis direction are denoted by X1 to X3, and theeffective pixel pitches in the Y-axis direction are denoted by Y1 to Y3.

When the effective pixel pitch in the X-axis direction defined asdescribed above is denoted by “SX” and the effective pixel pitch in theY-axis direction defined as described above is denoted by “SY”, a ratioSY/SX of the both effective pixel pitches is referred to as an “aspectratio”.

In the case of FIG. 4A, since the aspect ratio is “Y1/X1” and X1=Y1, theaspect ratio is 1. In the case of FIG. 4B, since the aspect ratio is“Y2/X2” and Y2>X1, the aspect ratio is larger than 1. In the case ofFIG. 4C, since the aspect ratio is “Y3/X3” and Y3<X3, the aspect ratiois smaller than 1.

In micro-convex lens structures of microlens arrays 91 to 94 illustratedin FIG. 5A to FIG. 5E, similarly to the cases of FIG. 4A to FIG. 4C, theeffective pixel pitches are defined as follows. In other words, theeffective pixel pitches in the X-axis direction and Y-axis direction are“X11 and Y11”, “X12 and Y12”, and “X13 and Y13” of FIG. 5A to FIG. 5D.

In the micro-convex lens structure of FIG. 5A, rectangle-shapedmicro-convex lenses 9111, 9112, . . . , 9121, and so on are arranged ina square matrix shape, and the aspect ratio is larger than 1.

In the microlens arrays 92 to 94 illustrated in FIG. 5B to FIG. 5E, themicro-convex lens structures are honeycomb-type arrays. In thehoneycomb-type arrays FIG. 5B through FIG. 5D, all the aspect ratios“Y12/X12” and “Y13/X13” are greater than 1.

In the “micro-convex lens” of any one of the four examples of themicro-convex lens structures illustrated in FIG. 5A to FIG. 5D, thelength in the Y-axis direction is larger than the length in the X-axisdirection.

In this manner, in the case of “the micro-convex lens having a shapewhere the length in the Y-axis direction is larger than the length inthe X-axis direction”, as the shape of the micro-convex lens, thecurvature in the X-axis direction is easily set to be larger than theY-directional curvature. Accordingly, the above-described “anamorphicoptical function where the power in the X-axis direction is greater thanthe power in the Y-axis direction” can be easily implemented.

For example, in the case of the example illustrated in FIG. 5A, as aspecific example, there is an example where X11=150 μm, Y11=200 μm, andaspect ratio=200/150=4/3>1. As a matter of course, in this case, thebeam diameter of the pixel displaying beam in the X-axis direction isset to be less than 150 μm, and beam diameter in the Y-axis direction isset to be less than 200 μm.

Any one of the arrays of micro-convex lenses FIG. 5B through FIG. 5D isa honeycomb-type array, and each micro-convex lens has a “elongatedshape in the Y-axis direction”.

The array of FIG. 5B is a “zigzag-type”, and any one of the arrays ofFIG. 5C and FIG. 5D is an “armchair-type”.

As a matter of course, any one of the “zigzag-type vertically-elongatedhoneycomb-type array” of FIG. 5B and the “armchair-typevertically-elongated honeycomb-type array” of FIGS. 5C and 5D can beavailable.

However, the array example of FIG. 5C has the following advantages incomparison with the array example of FIG. 5B.

In other words, in comparison with the array of FIG. 5B, in the array ofFIG. 5C, a “difference between the sizes in the X-axis direction and theY-axis direction” of the micro-convex lens is small, and a “differencebetween the effective pixel sizes” in the lateral and verticaldirections is small.

Specific sizes (numeric values) are given below. For example, in FIG.5B, with respect to the micro-convex lenses 9211, 9212, and the like,the lens diameter in the X-axis direction is set to be R2 x=100 μm, andthe lens diameter in the Y-axis direction is set to be R2 y=200 μm.

In such cases, the effective pixel pitch in the X-axis direction (=X12)becomes 50 μm, and the effective pixel pitch (=Y12) in the Y-axisdirection becomes 150 μm.

In a similar manner, in FIG. 5C, with respect to the micro-convex lenses9311, 9312, and the like, the lens diameter in the X-axis direction isset to be R3 x=100 μm, and the lens diameter in the Y-axis direction isset to be R3 y=200 μm.

The lengths of the upper and lower sides of the hexagon shapes of themicro-convex lenses 9311 and the like are set to be 50 μm.

In such cases, the effective pixel pitch (=X13) in the X-axis directionbecomes 75 μm, and the effective pixel pitch (=Y13) in the Y-axisdirection becomes 100 μm.

Accordingly, the “effective pixel pitches in the X-axis direction andthe Y-axis direction” of the case of the array (75 μm and 100 μm) ofFIG. 5C become “closer values” than those of the case of the array (50μm and 150 μm) of FIG. 5B.

In FIG. 5C and FIG. 5D, the effective pixel pitch in the X-axisdirection is denoted by X13, and the effective pixel pitch in the Y-axisdirection is denoted by Y13.

This is in accordance with the fact that, in the honeycomb-type arrays(armchair-type honeycomb-type arrays) of FIG. 5C and FIG. 5D, the pixelpitch in the X-axis direction and the pixel pitch in the Y-axisdirection are defined to be equal to each other.

In FIG. 5D, with respect to micro-convex lenses 9411, 9421, and thelike, the upper and lower sides parallel to the X-axis direction areshort, and the inclined sides are long.

As illustrated in these drawings, by deformation of the hexagon shape ofthe micro-convex lens, the pixel pitch in the X-axis direction X13 andthe pixel pitch in the Y-axis direction Y13 can be adjusted.

In the heads-up display illustrated in FIG. 1A, the pixel displayingbeam LC is perpendicularly incident on the micro-convex lens structureof the microlens array element 8.

However, the form of the incidence of the pixel displaying beam on themicrolens array element is not limited to the “perpendicular incidence”.

For example, in the case of miniaturizing the heads-up display bystudying arrangement of optical elements ranging from the light sourceunit to the reflection plane, an incidence form as illustrated in FIG.7A is considered.

In other words, in an example of FIG. 7A, the pixel displaying beam LCis incident to be inclined with respect to the microlens array element8.

In a case where the lens surface of the micro-convex lens is set to bean “aspherical surface”, the pixel displaying beam LC is incident to beinclined with respect to the optic axis of the aspherical surface, andthus, in some cases, the function of the aspherical surface cannot beimplemented.

In this case, similarly to a microlens array element 8 a of FIG. 7B, itis preferable that a lens surface optic axis AX of the micro-convex lensML is set to be inclined from the perpendicular direction with respectto a reference surface of the microlens array element 8 a.

By so doing, the lens surface optic axis AX can be allowed to beparallel to the incident direction of the pixel displaying beam LC or tobe close to the incident direction.

Note that the reference surface of the microlens array element 8 a is asurface of an array where the micro-convex lenses ML are arranged.

By doing so, the downsizing of the optical system or the improvement ofthe utilization efficiency of light can be implemented, so that the“divergence direction of the pixel displaying beam by the micro-convexlens” can be allowed to be homogenized.

The application of the HUD according to the example embodiment of thepresent disclosure is not limited to a car as described above, but theHUD may be applied to various kinds of operable mobile objects such astrains, ships, helicopters, and aircrafts. For example, a windshield(windbreak) of a motorbike can be configured as atransmitting/reflecting member.

In this case, a front windshield ahead of the cockpit may be configuredas a reflection plane.

As a matter of course, the HUD according to the present exampleembodiment may be implemented, for example, as an “image displayapparatus for movie viewing”.

The minute convex lenses in the minute convex lens arrangement diffusethe pixel displaying beam as described above, but may diffuse the pixeldisplaying beam only in one direction between the X direction and the Ydirection.

In such cases where diffusion is performed only in a single direction,“minute convex cylinder surface” may be applied to the lens surface ofthe minute convex lenses.

The shape of the minute convex lens may be shaped as a hexagon, and theminute convex lenses may be arranged like a honeycomb. Such variationsare conventionally known in the art of microlens array manufacturingmethod.

When the microlens array in which lenses are periodically arranged isused as a microlens array element, such as a transmissive screen or areflective screen, of an optical device, e.g., a HUD, an interferencepattern such as moire and diffraction pattern due to diffracted lightthat is strengthened in a certain direction is visually recognized onthe microlens array, which is known in the art. In other words, theoccurrence of such an interference pattern reduces the visibility of animage and a virtual image formed by the microlens array element.

In the present embodiment, the expression “the microlens array in whichlenses are periodically arranged” refers to a microlens array(hereinafter, referred to also as a periodically-arranged lens array)with the pitch (hereinafter, referred to as a lens pitch) of vertices ofa plurality of microlenses, i.e., the distance between the vertices ofadjacent microlenses is periodic (for example, constant).

The “vertices of the microlenses” refers to the position of the vertexof a lens surface of each microlens within the XY plane. The “vertex ofa lens surface of each microlens” refers to a point at which the lenssurface of each microlens intersects with the optic axis (which isparallel with the Z axis in the present embodiment) of the microlens.

Specific examples of the periodically-arranged lens array include a lensarray in which the vertex (i.e., the position at which the length in theZ-axis direction is maximum) of each microlens coincides with the centerof gravity of each microlens, the pitch (lens pitch) of the vertices(the centers of gravity) of microlenses are constant, and the lensdiameter (lens size) of each microlens is constant. In the presentembodiment, the optic axis of each microlens passes through the centerof gravity of the microlens. In such a case, a fringe pattern in whichthe interference pattern, the direction of interference fringe, and thepitches are uniformly formed, is visually recognized.

The “center of gravity of each microlens” refers to the position of thegravity of a microlens projected onto the XY plane.

In an example periodically-arranged lens array, a plurality ofmicrolenses each having a rectangular planar shape of the same size arearranged such that the lens pitch of the plurality of microlenses isconstant. In such a lens array, interference fringes are visuallyrecognized in both a horizontal direction and a vertical direction. Inanother example periodically-arranged lens array, a plurality ofmicrolenses each having a hexagon-honeycomb planar shape of the samesize are arranged such that the lens pitch of the plurality ofmicrolenses is constant. In such a lens array, interference fringes arevisually recognized in three directions of sixfold symmetry.

In view of the above, using the microlens array with each microlenshaving a lens diameter equal to or larger than a beam diameter canreduce or prevent the interference of diverging beams emitted fromadjacent microlenses. However, even with the use of such a microlensarray, very little interference still remains due to the widelyspreading of the diverging beams, which is visually recognized as theinterference pattern with a high visibility because the direction andthe pitch of the interference pattern are uniformed.

To reduce the occurrence of such an interference pattern, theperiodicity of the interference pattern is removed to reduce thevisibility of the interference pattern.

As described above, the periodic interference pattern with uniformedpitch and direction occurs in the periodically-arranged lens array dueto the periodic arrangement of microlenses. Accordingly, removing theperiodicity of the lens (microlens) arrangement of the microlens array,i.e., making the lens pitch random (non-periodic), can reduce or preventthe occurrence of the interference pattern.

FIG. 8 is an illustration of a microlens array (hereinafter, referred toalso as a randomly-arranged lens array) with randomized lens pitches.Such a randomly-arranged lens array has a structure obtained by randomlyshifting (offsetting) the optic axis of each microlens to a directionperpendicular to the optic axis (the Z axis) of theperiodically-arranged lens array in which the vertex of each microlenscoincides with the center of gravity thereof. In other words, therandomly-arranged lens array has a structure in which the lens pitchesare irregular. In this case, the optic axis of each microlens passesthrough the vertex of the same microlens, failing to pass through thecenter of gravity of the same microlens. Note that, the center ofgravity of each microlens of the randomly-arranged lens array in FIG. 8may be the center of a circle that passes through at least three pointsat the outer edge of the same microlens and encloses the same microlens.Alternatively, in some embodiments, the center of gravity of eachmicrolens of the randomly-arranged lens array in FIG. 8 may be thecenter of a circle that contacts at least three sides of the samemicrolens and is enclosed by the same microlens.

In such a microlens array in which the lens pitches and the directionsof borderlines between microlenses are randomized (non-periodic) asillustrated in FIG. 8 for example, an interference pattern that occursbetween adjacent microlenses 861 and 862 or adjacent microlenses 862 and863 has different directions and pitches, which is not visuallyrecognized as the interference pattern having uniformed direction andpitch when macroscopically observed. That is, randomizing the lenspitches of microlenses reduces the occurrence of an interferencepattern, and randomizing the directions of borderlines betweenmicrolenses disperses the interference intensity of diverging beams(hereinafter, referred to also as adjacent diverging beams) emitted fromadjacent microlenses.

In the randomly-arranged lens array in FIG. 8, for example, lens pitchesp1 through p29 all may differ from each other. Alternatively, some ofthe lens pitches p1 through p29 may be the same and the remainingpitches may differ from each other. In other words, therandomly-arranged lens array according to at least one embodiment issatisfactory as long as the lens pitches are irregular. In FIG. 8, ablack dot refers to the vertex of each microlens. Further, a blacksquare refers to the center of gravity of each microlens.

Preferably, the lens pitches ( . . . p4, p9, p11 . . . ), ( . . . p23,p24, p25 . . . ), ( . . . p8, p12, p20 . . . ), and so on, each set ofwhich is arranged in the same direction of lens arrangement, areirregular (non-periodic).

The microlens array element made of resin, such as the microlens arrayelement 8, is produced by injection molding. The injection molding isperformed by using an injection molding device and a mold as cited onthe website http://www.polyplastics.com/jp/support/mold/outline/.

The injection molding device includes a mold clamping unit and aninjection unit. The mold clamping unit opens and closes the mold, andprojects the mold. The mold clamping unit has a toggle system and adirect-pressure system that directly opens and closes the mold by ahydraulic cylinder.

The injection unit heats and melts resin (thermoplastic resin) to injectthe resin into the mold. More specifically, the injection unit causes amotor to rotate a screw within a cylinder, and collects (which isreferred to as “measurement”) resin supplied to the cylinder through ahopper in the front part of the screw, up to the stroke equivalent to adetermined amount of resin, injecting the collected resin. The injectionunit controls the speed of movement of the screw (injection speed) whileresin flows within the mold, and controls pressure (hold pressure) afterthe resin is filled in the mold. The injection unit is designed toswitch between a speed control and a pressure control when the screwreaches a given position or the pressure reaches a given injectionpressure.

The mold includes a lens arrangement forming unit and a gate unit. Thelens arrangement forming unit has a transfer surface formed over theinner wall surface to form a lens arrangement area having asubstantially flat-plate shape. The lens arrangement area has aplurality of micro-convex lenses (microlenses) two-dimensionallyarranged over the entire surface thereof in the microlens array element.The gate unit allows resin to be supplied into the lens arrangement areaforming unit. The gate unit has an entrance coupled to the exit of thecylinder of the injection unit. Note that a plurality of microlenseshaving a circular or elliptic shape is arranged in matrix (asquare-matrix) in the planar view.

A description is given of a method for forming a microlens array elementaccording to a comparative example by injection molding, referring toFIG. 10A through FIG. 10D. Note that a mold for forming a microlensarray element according to the comparative example has a gate unithaving a straight shape (a rectangular shape in a planar view) (see FIG.10B). The expression “planar view” refers to a view when viewed from theZ-axis direction that is a normal direction that passes through thecenter of the lens arrangement area in the present disclosure.

Firstly, a mold clamping process is performed (see FIG. 10A). Morespecifically, a mold clamping unit presses the lens arrangement areaforming unit against the gate unit so that the mold is closed.

Next, an injection process is performed (see FIG. 10B). Morespecifically, the injection unit injects heated and melted resinmaterial into the mold. The resin flows within the mold as indicated byarrows in FIG. 10B.

Next, a pressure-holding, cooling and solidifying processes areperformed (see FIG. 10C).

Finally, the mold is opened and a molded product is taken out. Morespecifically, the mold clamping unit moves away the lens arrangementarea forming unit from the gate unit so that the mold is opened and themolded product is ejected from the mold. Thus, a molded product, i.e., amicrolens array element according to the comparative example, isobtained that includes a lens arrangement area having a rectangularshape in the planar view and a gate area having a rectangular shape inthe planar view. The gate area is formed in the gate unit, having ashape (the rectangular shape in the planar view) that corresponds to theshape of the inner wall surface of the gate unit.

In the injecting method according to the comparative example, the resinirregularly (ununiformly) flows at a corner on a −X side and a +Y sideand at another corner on the −X side and a −Y side within the lensarrangement forming unit (the forming unit) (see FIG. 10B) in theprocess of filling the mold with resin under high pressure. This causesa large deformation at corresponding positions in the molded product asindicated by shaded circles in FIG. 10C and FIG. 10D.

Accordingly, the present inventors have conceived of a mold M with agate unit G having an improved-shaped passage for inserting resin intothe mold M. More specifically, the inner wall surface of the gate unit Gof the mold M has a shape (for example, an isosceles trapezoid shape)that gradually increases in width (Y-axis-directional width) in adirection that approaches a lens arrangement area forming unit F (aforming unit) in the planar view, i.e., viewed from the Z-axis direction(see FIG. 11A through FIG. 11D). Hereinafter, such a mold M is referredto as an improved mold M. In the present embodiment, injection moldingis performed using the improved mold M.

The following describes an injection molding method using an improvedmold M according to the present embodiment, referring to FIG. 11. Thesteps of the injection molding method using the improved mold M isbasically the same as those illustrated in FIG. 10A through FIG. 10D.FIG. 11A through FIG. 11D correspond to FIG. 10A through FIG. 10D,respectively.

In the injection process (see FIG. 11B), resin regularly (uniformly)flows within the improved mold M (see arrows in FIG. 11B). As a result,no deformation occurs in a molded product according to the presentembodiment (see FIG. 11C and FIG. 11D) unlike the molded productaccording to the comparative example. The molded product according tothe present embodiment includes a lens arrangement area LA having arectangular shape in the planar view and a gate area GA having anisosceles trapezoid shape in the planar view. The gate area GA is formedin the gate unit G, having a shape (the isosceles trapezoid shape in theplanar view) that corresponds to the shape of the inner wall surface ofthe gate unit G.

FIG. 12A and FIG. 12B are illustrations of the microlens array elementaccording to the comparative example and the microlens array element 8according to the present embodiment, respectively. As illustrated inFIG. 12A and FIG. 12B, each microlens array element includes a lensarrangement area and a gate area, which are adjacent to each other. InFIG. 12A, the shaded circles represent areas in which deformation occursin the lens arrangement area according to the comparative example.

More specifically, each of the lens arrangement area according to thecomparative example and the lens arrangement area LA according to thepresent embodiment has a rectangular area having a first side with alength a that is parallel to the X axis and a second side with a lengthb that is parallel to the Y axis in the planar view (when viewed fromthe Z-axis direction). The length a is longer than the length b.

In the comparative example, the gate area is an area having arectangular shape in the planar view. The gate area is disposed on the−X side of the lens arrangement area, and the +X-side edge of the gatearea is attached to the center part (an area other than ends) of the −Xside of the second side of the lens arrangement area. That is, thelength c in the Y-axis direction of the gate area according to thecomparative example is constant. Further, the length c is shorter thanthe length b.

In the present embodiment, the gate area GA is disposed on the −X sideof the lens arrangement area LA, and the +X-side edge of the gate areaGA is attached to the −X-side second side of the lens arrangement areaLA. The gate area GA according to the present embodiment graduallyincreases in Y-axis-directional width in a direction that approaches thelens arrangement area LA. That is, the gate area GA according to thepresent embodiment has a tapered shape.

More specifically, the gate area GA according to the present embodimenthas an isosceles trapezoid shape in the planar view. The lower base ofthe isosceles trapezoid shape (the gate area GA) coincides with thesecond side of the lens arrangement area LA. That is, the lower base ofthe gate area GA according to the present embodiment has the length b.The upper base of the gate area GA according to the present embodimenthas the length c. The Y-axis-directional width at the −X-side edge ofthe gate area GA is common between the comparative example and thepresent embodiment, and the Y-axis-directional width at the +X-side edgeof the gate area GA differs between the comparative example and thepresent embodiment. The gate area GA according to the comparativeexample has the Y-axis-directional width that is constant from the−X-side edge to the +X-side edge of the gate area. In contrast, the gatearea GA according to the present embodiment has the Y-axis-directionalwidth that monotonically increases in a direction from the −X-side edgeto the +X-side edge of the gate area GA.

FIG. 13A illustrates an analysis result of the presence or absence ofdeformation in the lens arrangement area of the microlens array element(molded product) according to the comparative example. In thecomparative example, a very large degree of deformation is confirmed inareas enclosed by dashed circles in FIG. 13A.

Such a deformation causes an increase in shift of the orientation of theoptic axis in double refraction to be described later. When a microlensarray element with such a shift in the orientation of the optic axis indouble refraction is used in the image display apparatus 1000 in FIG. 1to generate a virtual image based on image data of the white color, itis recognized that the generated virtual image represents light pinkcolor in areas corresponding to the areas of deformation in themicrolens array element.

FIG. 13B illustrates an analysis result of the presence or absence ofdeformation in the lens arrangement area LA of the microlens arrayelement 8 (molded product) according to the present embodiment. In thepresent embodiment, any remarkable deformation is not confirmed over thewhole lens arrangement area LA.

That is, using the improved mold M to produce the microlens arrayelement 8 according to the present embodiment allows resin to regularly(uniformly) flow within the improved mold M, resulting in an effectivereduction in occurrence of deformation of a molded product.

When the microlens array element 8 thus obtained by using such animproved mold M is used in the image display apparatus 1000 in FIG. 1 togenerate a virtual image based on image data of the white color, it isrecognized that a desired white color is achieved over the generatedvirtual image as a whole.

Note that the gate area GA is secondarily formed with the formation ofthe lens arrangement area LA in the molded product. Accordingly, thegate area GA, which does not contribute to the function of the microlensarray element 8, may be removed by cutting or sanding to downsize themicrolens array element 8.

In the above description, the cases where the microlens array element 8with the lens arrangement area LA having a substantially flat-plateshape is produced by injection molding, using the improved mold M aredescribed. However, no limitation is intended herein. In someembodiments, the lens arrangement area LA may be curved along the X-axisdirection in the microlens array element 8 produced using the improvedmold M as illustrated in FIG. 14. Such a microlens array element 8curved along the X-axis direction has an advantageous effect thatreduces the difference in optical-path length from the two-dimensionaldeflector 6 to a microlens between the microlenses when light deflectedby the two-dimensional deflector 6 directly enters the microlens arrayelement 8 without hitting the concave-surface mirror 7. In some otherembodiments, the microlens array element 8 produced by using theimproved mold M may be curved along, for example, the Y-axis directionin addition to or in place of the X-axis direction.

In such a case, the microlens array element 8 is projected onto avirtual plane S perpendicular to the normal line η of the center of thelens arrangement area LA of the microlens array element 8, and aprojection image a (for example, a rectangular shape) thus obtained isassumed as the above-described substantially flat-plate shaped microlensarray element 8. Note that the inner wall surface of the lensarrangement area forming unit F of the mold M is preferably curved toproduce the curved microlens array element 8.

As described above, the present inventors have found that the microlensarray element 8 produced by using the improved mold M according to thepresent embodiment has an advantageous effect that reduces or prevents ashift in orientation of the optic axis in double refraction, thusincreasing the optical properties. The “optic axis” is referred to alsoas a main axis (a fast axis or a slow axis) of the double refraction.The “shift in orientation of the optic axis” is referred to also as avariation in orientation of the optic axis.

The “shift in orientation of the optic axis” is defined as an angle θformed by the orientation of the optic axis and the polarizationdirection (hereinafter, referred to also as a “reference orientationRO”) of linearly polarized light (a laser light that has hit theconcave-surface mirror 7) that enters the lens arrangement area LA ofthe microlens array element 8 (see FIG. 21). As a device for measuringdouble refraction, the birefringence measurement system produced byHINDS Instruments is used, for example, as cited on the website ofhttp://www.hindsinstruments.com/products/birefringence-measurement-systems/.For example, two polarization elements are disposed at the entrance sideand the exit side of the microlens array, respectively, and thesepolarization elements are rotated in synchronization by, e.g., a motor,with a fixed ratio in rotational angle between these polarizationelements, thereby obtaining a signal in which multiple periods aremixed. This obtained signal is analyzed to thus measure the doublerefraction (birefringence). The “polarization direction” refers to avibration direction of the electric field of the linearly polarizedlight. The orientation of the optic axis is defined for each microlensof the microlens array element 8. The polarization direction of thelinearly polarized light that enters the microlens array element 8 isalso defined for each microlens of the microlens array element 8.

For example, the polarization direction of light (linearly polarizedlight) emitted from the light-source unit 100 is originally set to theY-axis direction. The polarization direction of some rays of thelinearly polarized light other than rays that enter the microlens arrayelement 8 rotates within an XY plane, thereby to shift from the Y-axisdirection as the linearly polarized light is deflected by thetwo-dimensional deflector 6.

In general, the double refraction is described in terms of theretardation (phase difference) and the optic axis (the fast axis or theslow axis). Whether the main-axis orientation MO of the doublerefraction is the fast-axis orientation or the slow-axis orientationdepends on the property of resin material for the microlens arrayelement. Double refraction is, as known in the field of optics, theseparation of a ray of light into two unequally refracted,plane-polarized rays of orthogonal polarizations, occurring in crystalsin which the velocity of light rays is not the same in all directions.

In this case, the retardation (phase difference) is described in termsof two linearly polarized light beams having polarization directionsperpendicular to each other, of the linearly polarized light that haspassed through the lens arrangement area LA of the microlens arrayelement 8.

More specifically, the slow-axis orientation is the polarizationdirection of one of the two linearly polarized light beams that slowlytravels and is delayed in phase with reference to the linearly polarizedlight that has entered the lens arrangement area LA. The fast-axisorientation is the polarization direction of the other beam of the twolinearly polarized light beams that travels fast and accelerates thephase with reference to the linearly polarized light that has enteredthe lens arrangement area LA. The retardation satisfies the followingconditional expressions where Na denotes a refractive index of the slowaxis of the microlens array element 8 with respect to the referenceorientation RO (the polarization direction of the linearly polarizedlight that enters the lens arrangement area LA of the microlens arrayelement 8, Nb denotes a refractive index of the fast axis with respectto the reference orientation RO (Na is larger than Nb), d denotes athickness of the microlens array element 8, R denote retardation, and ΔNdenotes double refraction: R=ΔN·d (nm)=ΔN·d·360/λ (deg), and ΔN=Na−Nb.

Here, some microlens array elements 8 were prepared under variousmolding conditions, such as the pressure applied to the mold M and thetemperature of the mold M, and the speed of injecting resin. Theprepared microlens array elements 8 were mounted on the image displayapparatus 1000 in FIG. 1, and virtual images were formed based on imagedata of the white color. Such a virtual image was analyzed to determinewhich area achieves the white color and which area fails to achieve thewhite color in the lens arrangement area LA using the processes in FIG.15A through 15C. In FIG. 15A through 15C, the x-y coordinates of aplurality of points are (x1, y1), (x2, y2), (x3, y3), and (x4, y4) inthe lens arrangement area LA of the microlens array element 8. In thiscase, although only the above-described four points are represented inFIG. 15A through 15C, the microlens array element 8 is actually dividedinto approximately 15000 sections for analysis.

In the present disclosure, the expression “achieves the white color” isdefined to mean that a measured chromaticity coordinate falls within acircle having a radius of 0.015, of which the center is the center ofthe white color, in the Ua-Va chromaticity coordinate system in FIG.15B. Hereinafter, the above-described circle having the radius of 0.015is referred to also as a “white-colored permissible circle”. As can beseen from FIG. 15B, the coordinates (x2, y2), (x3, y3), and (x4, y4) arewithin the white-colored permissible circle, and the coordinate (x1, y1)is outside the white-colored permissible circle.

Note that the “center of the white color” may be (⅓, ⅓) in the x-ychromaticity coordinate system. Alternatively, the coordinate of the“center of the white color” may be determined by sensory assessment. Asthe coordinate of the center of the white color in the x-y chromaticitycoordinate system to recognize the white color differs by a human race,the coordinate may be determined as appropriate.

FIG. 16 is a graph of a relation between the retardation and the shiftin orientation of the optic axis in the microlens array elementaccording to the comparative example. In FIG. 16, the referenceorientation RO (the polarization direction of the linearly polarizedlight) is designated as 0°. FIG. 17 is an illustration of a chromaticitymap of the Ua-Va chromaticity coordinates measured from the virtualimage generated based on the image data of the white color using themicrolens array element according to the comparative example. It hasbeen found by the present inventors that, the range that achieves thewhite color in the virtual image (the range of the Ua-Va chromaticitycoordinates that fall within the white-colored permissible circle inFIG. 17) refers to the range represented by two dark-colored dashedlines in FIG. 16, i.e., the zone in which the shift (θ) in orientationof the optic axis falls within the range of ±20° (ranges from −20° to+20°). More specifically, the range that achieves the white color in thevirtual image is, for example, the zone in which the shift (θ) in theslow-axis orientation falls within the range of ±20° when the main-axisorientation MO of the double refraction is the slow-axis. In contrast,it has been found by the present inventors that the range that fails toachieve the white color in the virtual image (the range of the Ua-Vachromaticity coordinates that fall outside the white-colored permissiblecircle in FIG. 17) is another zone in which the shift (θ) in orientationof the optic axis falls outside the range of ±20°. The same applies tothe case where the main-axis orientation of the double refraction is,for example, the fast-axis orientation.

As described above, the microlens array element 8 according to thepresent embodiment produced by using the improved mold M reduces theoccurrence of deformation, thereby increasing the optical properties ofthe microlens array element 8. Accordingly, the position and posture ofthe microlens array element 8 are adjusted with reference to thereference orientation RO (the polarization direction of the linearlypolarized light that enters the lens arrangement area LA of themicrolens array element 8), thereby to allow the shift (θ) inorientation of the optic axis to fall within the range of ±20° over thewhole lens arrangement area LA (all of the microlenses). In other words,it has been found by the present inventors that there is the referenceorientation RO (the polarization direction of the linearly polarizedlight that enters the microlens array element 8) that allows the shift(θ) in orientation of the optic axis to fall within the range of ±20°over the whole lens arrangement area LA (all of the microlenses). It hasbeen confirmed that the white color was achieved over the whole area ofa virtual image generated by the image display apparatus 1000 equippedwith the microlens array element 8 according to the present embodiment(see FIG. 18 and FIG. 19), compared to the comparative example of FIG.16 and FIG. 17.

Note that the white color has a very small range in which human eyeidentifies a color as compared to other colors, such as the red color,the green color, and the blue color. That is, the white-coloredpermissible circle has a much smaller radius than those of thered-colored permissible circle, the green-colored permissible circle,and the blue-colored permissible circle. In short, achieving the whitecolor over the whole area in the virtual image means achieving anydesired color other than the white color over the whole area of thevirtual image.

As can be seen from FIG. 16 and FIG. 18, the retardation values widelyranges, which is difficult to control with the molding conditions (forexample, pressure applied to and the temperature of the mold M and theinjection speed of resin) or the shape (for example, a tapered shape) ofthe gate unit G of the mold M.

In short, controlling the orientation of the optic axis can effectivelyincrease the optical properties of the lens arrangement area LA of themicrolens array element 8, irrespective of resin material.

Note that the shapes of the inner wall of the gate unit G and the gatearea GA of the microlens array element 8 are not limited to theisosceles trapezoid shape in the planar view, and each may be a shapethat gradually or in a stepwise manner increases in Y-axis-directionalwidth in a direction that approaches the lens arrangement area formingunit F and the lens arrangement area LA in the planar view.

As illustrated in FIG. 20A for example, the +X-side edge (the exit ofthe gate unit G) of the inner wall of the gate unit G may have theY-axis-directional width that is smaller than the Y-axis-directionalwidth of the inner wall of the lens arrangement area forming unit F. Inother words, the Y-axis-directional width (maximum width as theY-axis-directional width of the gate area GA) of +X-side edge of thegate area GA may be smaller than the Y-axis-directional width of thelens arrangement area LA.

As illustrated in FIG. 20B for another example, the +Y-side and −Y-sideinner walls of the gate unit G and the +Y-side and −Y-side side surfacesof the gate area GA may be curbed.

As illustrated in FIG. 20C for still another example, the +Y-side and−Y-side inner walls of the gate unit G and the +Y-side and −Y-side sidesurfaces of the gate area GA may be partially parallel to the XZ plane.

As described above, each microlens of the microlens array element 8according to the present embodiment, which is made of resin, satisfiesconditional expression below where θ denotes an angle formed by theorientation of the optic axis (the main-axis orientation MO of doublerefraction) and the reference orientation RO (the polarization directionof the linearly polarized light that enters the microlens array element8) in the lens arrangement area LA of the microlens array element 8:

−20°≤θ≤20°.

Preferably, the above-described conditional expression is satisfied overthe whole area of the lens arrangement area LA.

The microlens array element 8 according to the present embodiment, whichis made of resin, includes the lens arrangement area LA and the gatearea GA, which are adjacent to each other. In this case, the gate areaGA has the Y-axis-directional width (see FIG. 11A through FIG. 11D) thatgradually increases in a direction that approaches the lens arrangementarea LA in the planar view. In other words, the microlens array element8 is produced by injection molded using the improved mold according tothe present embodiment.

The microlens array element 8 according to the present embodiment canincrease the optical properties.

In some embodiments, the gate area GA may have a Y-axis-directionalwidth that increases in a stepwise manner in the direction thatapproaches the lens arrangement area LA in the planar view. In someembodiments, the gate area GA may have a +Y-side surface and a −Y-sidesurface that are tilted (tilted surfaces) or curved (curved surfaces).The width between the +Y-side surface and the −Y-side surface increasesin the direction that approaches the lens arrangement area LA in theplanar view. In this configuration, the tilt angle of each tiltedsurface and the radius of curvature of each curved surface each isdetermined by the shape of the inner wall of the gate unit G of theimproved mold M.

Preferably, the gate area GA has a maximum width (in the Y-axisdirection) that is smaller than or equal to the length of the edge (the−X-side edge of the lens arrangement area LA) on the side of the gatearea GA of the lens arrangement area LA in the planar view. Morepreferably, the maximum width of the gate area GA is equal to the widthof the edge on the side of the gate area GA of the lens arrangement areaLA.

In some other embodiments, the lens arrangement area LA may be curvedalong at least one direction (for example, the X-axis direction or theY-axis direction).

Preferably, the lens arrangement area LA has a rectangular shape having,on the side of the gate area GA (on the −X side of the lens arrangementarea LA), an edge shorter than another edge in the planar view. Thisconfiguration can downsize the gate area GA. In some embodiments, thelens arrangement area LA may have any shape other than the rectangularshape in the planar view.

In the present embodiment, the lens arrangement area LA is an area inwhich a plurality of microlenses is arranged in array.

The image display apparatus 1000 includes the light-source unit 100including a semiconductor laser (a light source to emit linearlypolarized light), the two-dimensional deflector 6 (an image formingelement), and the microlens array element 8 (a microlens array)including a lens arrangement area LA. The light for forming an imageenters the lens arrangement area LA. This configuration can display animage of desired color. The reference orientation RO coincides with thepolarization direction of the light (the linearly polarized light) forforming an image.

The image display apparatus 1000 includes a plurality of semiconductorlasers. The light-source unit 100 further includes a beam combiningprism 101 (a combiner) to combine light beams emitted from the pluralityof semiconductor lasers. The chromaticity coordinates over the wholearea of an image fall within a circle (the white-colored permissiblecircle) having a radius of 0.015, of which the center is the center ofthe white color, in the chromaticity coordinate system. The image isformed by driving the plurality of semiconductor lasers based on theimage data of the white color.

The image display apparatus 1000 further includes a concave mirror 9 (alight emitter) to cause light having passed through the microlens arrayelement 8 to travel to the transmission and reflection member 10. Thisconfiguration can display a virtual image of desired color.

An object apparatus O including the image display apparatus 1000 and amobile object equipped with the image display apparatus 1000 can provideinformation of a virtual image with a good reproducibility to apassenger in the mobile object.

An improved mold M according to the present embodiment is a mold toproduce a microlens array element 8 by injection molding. The improvedmold M includes a lens arrangement forming unit F (a forming unit) toform a lens arrangement area LA of the microlens array element 8 and agate unit G to let resin into the lens arrangement area forming unit F.The gate unit G has an inner wall that gradually increases in width in adirection that approaches the lens arrangement area forming unit F inthe planar view.

This configuration can prevent or reduce the occurrence of deformationin the lens arrangement area LA of the microlen array element 8produced.

In some embodiments, the gate area GA may have a Y-axis-directionalwidth that increases in a stepwise manner in the direction thatapproaches the lens arrangement area LA in the planar view. In someembodiments, the gate unit G may have a +Y-side inner-wall surface and a−Y-side inner-wall surface that are tilted (tilted surfaces) or curved(curved surfaces). The width between the +Y-side inner-wall surface andthe −Y-side inner-wall surface increases in the direction thatapproaches the lens arrangement area LA in the planar view. In thisconfiguration, the tilt angle of each tilted surface and the radius ofcurvature of each curved surface may be changed as appropriate accordingto the molding conditions, such as the pressure applied to the mold Mand the temperature of the mold M, the injection speed of the resin, andso on).

Preferably, the inner wall of the gate unit G has a maximum width (theY-axis-directional width) that is less than or equal to the width of theedge on the side of the gate unit G (on the −X side) of the lensarrangement forming unit F. More preferably, the inner wall of the gateunit G is equal to the width of the edge of the gate unit G of the lensarrangement forming unit G.

In some embodiments, the lens arrangement area forming unit F may becurved along at least one direction (for example, the X-axis directionor the Y-axis direction).

Preferably, the inner wall of the lens arrangement area forming unit Fmay have a rectangular shape having, on the side of the gate unit G (the−X side) of the lens arrangement area forming unit F, an edge shorterthan another edge in the planar view. This configuration can downsizethe gate unit G. In some embodiments, the lens arrangement area formingunit F may have any shape other than the rectangular shape in the planarview, according to the lens arrangement area LA to be formed.

The microlens array element 8 produced using the improved mold Maccording to the present embodiment can increase the optical properties.

In the present embodiment, the two-dimensional deflector 6 as an imageforming element to form an image on the microlens array element 8 isconstituted by the MEMS mirrors. However, no limitation is intendedherein. Alternatively, in some embodiments, the two-dimensionaldeflector 6 may be constituted by any other type of mirror such as agalvano mirror.

In the present embodiment, a semiconductor laser is used as a lightsource. However, no limitation is intended herein. Any light source thatemits linearly polarized light is available.

In the example embodiment described above, a color image is generated.However, no limitation is indicated therein, and a monochrome image maybe generated instead of the color image.

The transmission and reflection member may be made of a material otherthan that of the front windshield of a mobile object, and may bearranged between the front windshield and an observer, for example, likea combiner.

The image display apparatus according to the present disclosure mayadopt a panel system as the HUD projection method, instead of theabove-described laser scanning system. In the panel system, an imageforming element, such as a liquid crystal display (LCD), a digitalmicro-mirror device (DMD) panel (digital mirror device panel), or avacuum fluorescent display (VFD), is used to form an intermediate image.Note that, unlike the panel type where the image is formed by partiallylight blocking over the entire screen emission, since emitting ornon-emitting can be assigned to each pixel, a high-contrast image can beformed in general.

The image display apparatus according to the present disclosure isapplicable not only to a HUD, which is mounted on a mobile object, butalso to, for example, a head-mounted display that is mounted on the headof an observer, a prompter, and a projector.

Thus, the embodiments of the present disclosure may be applied to animage display apparatus including a microlens array element made ofresin.

Further, the embodiments of the present disclosure are effectiveparticularly in a microlens array element that is less likely to causethe occurrence of speckle noise. However, no limitation is intendedherein. The present disclosure is also applicable in a screen membersuch as a diffuser panel.

In the above-described embodiment, cases in which the image displayapparatus is provided for a mobile object such as a vehicle, anaircraft, a ship, and a mobile object, such as a robot, were described.However, no limitation is indicated thereby, and modification may bemade as long as the image display apparatus is provided for an object.The term “object” includes not only a mobile object but also an objectthat is located on a permanent basis or an object that is transportable.

Hereinafter, a description is provided of process of thinking, in whichthe inventor has conceived of the above-described embodiments.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the above teachings, the present disclosure may bepracticed otherwise than as specifically described herein. With someembodiments having thus been described, it will be obvious that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the scope of the present disclosure and appended claims,and all such modifications are intended to be included within the scopeof the present disclosure and appended claims.

What is claimed is:
 1. An apparatus comprising: a light source to emitthe light; an image forming element to form an image with the lightemitted from the light source; and a microlens array comprising: Nlenses ranging from a 1^(st) lens to an N^(th) lens, N being a positiveinteger; and a lens arrangement area having the N lenses arranged inarray, the lens arrangement area to receive light emitted from a lightsource, at least one of the N lenses satisfying a conditional expressionbelow:−20°≤θ≤20° where θ denotes an angle formed by a main-axis orientation ofdouble refraction and a reference orientation, wherein at least a partof the lens arrangement area is irradiated with the light for formingthe image.
 2. The apparatus according to claim 1, wherein thelight-source unit includes a light source to emit the light that islinearly polarized, and wherein the reference orientation is apolarization direction of the light for forming the image.
 3. Theapparatus according to claim 1, wherein the light-source unit includes aplurality of light sources constituted by the light source and at leastanother light source, wherein the light-source unit further includes acombiner to combine light beams emitted from the plurality of lightsources into one light beam, and wherein chromaticity coordinates over awhole area of an image, which are formed with light beams emitted fromthe plurality of light sources based on image data of a white color,fall within a circle having a radius of 0.015 and having a center at acenter of the white color in a chromaticity coordinate system.
 4. Theapparatus according to claim 1, further comprising: a light emitter toproject the light having passed through the microlens array; and atransmission and reflection member to make the light projected from thelight emitter viewable.
 5. An object apparatus comprising: the apparatusaccording to claim 4; and an object equipped with the apparatus.
 6. Theobject apparatus according to claim 5, wherein the object is a mobileobject, and wherein the transmission and reflection member is awindshield mounted on the mobile object.
 7. An apparatus comprising: alight source to emit light, the light being polarized; an image formingelement to form an image with the light emitted from the light source;and a screen having N lenses arranged in array, N being a positiveinteger, the screen having an optically effective area through which thelight for forming the image passes, the N lenses ranging from a 1^(st)lens to an N^(th) lens, at least one of the N lenses of the screensatisfying a conditional expression below:−20°≤θ≤20° where θ denotes an angle formed by a main-axis orientation ofdouble refraction and a polarization direction of the light beam.
 8. Theapparatus according to claim 7, wherein the screen includes a microlensarray having a lens arrangement area including the N lenses, and whereinthe optically-effective area is at least a part of the lens arrangementarea.
 9. The apparatus according to claim 7, wherein the light sourceincludes a plurality of light sources, wherein the light source furtherincludes a combiner to combine light beams emitted from the plurality oflight sources into one light beam, and wherein chromaticity coordinatesover a whole area of an image, which are formed with light beams emittedfrom the plurality of light sources based on image data of a whitecolor, fall within a circle having a radius of 0.015 and having a centerat a center of the white color in a chromaticity coordinate system. 10.The apparatus according to claim 7, further comprising: a light emitterto project the light having passed through the screen; and atransmission and reflection member to make the light projected from thelight emitter viewable.
 11. A mold for producing a microlens array byinjection molding comprising: a lens section to form a lens arrangementarea, in which a plurality of lenses are to be formed, of a microlensarray; and a gate section to let resin in the lens section, the gatesection having an inner wall that increases in width in a direction thatapproaches the lens section in a planar view.
 12. The mold according toclaim 11, wherein the inner wall of the gate section has a maximum widththat is less than or equal to a width of an edge on a side of the lenssection which is adjacent to the gate section.
 13. The mold according toclaim 11, wherein an inner wall of the lens section has a rectangularshape having, on a side of the gate section, an edge shorter thananother edge in the planar view.
 14. A microlens array molded using themold according to claim
 11. 15. A method of displaying an image,comprising: generating polarized light; irradiating the polarized lightthrough a screen including a plurality of lenses in an array; displayingan image using the polarized light which has passed through the screen,wherein each of the plurality of lenses satisfies:−20°≤θ≤20° where θ denotes an angle formed by a main-axis orientation ofdouble refraction and a polarization direction of the polarized light.